1. Field of the Invention
The present invention relates to a system on chip (SoC) structure, a duplexer, and a duplexer fabrication method thereof and, more particularly, to a SoC structure including an air cavity for isolating elements, a duplexer, and a duplexer fabrication method thereof.
2. Description of the Related Art
The demands for compact, multifunction electronic devices have been suddenly increased with the development of electronic technology. Thus, SoC technology has been introduced. SoC means technology for integrating a plurality of elements into one chip so as to realize one system. Chips fabricated using SoC technology are called SoC structures. In particular, efforts to fabricate various types of chips in the form of SoC have been made with the introduction of Micro-Electro-Mechanical Systems (MEMS) technology.
However, if a plurality of elements are integrated on one substrate, the possibility of interferences among the elements occurring is great. Also, if an element is driven, heat generated from the element may be transmitted through the substrate to another element so that the heat affects another element. Thus, SoC structures may malfunction during driving.
Various types of cellular phones, personal digital assistants (PDAs), note books, and the like have been developed and popularized with the development of radio communication technology. Such portable communication devices necessarily use duplexers. Such a duplexer as a kind of representative element complexly using a filter appropriately splits signals transmitted and received through an antenna in a communication system realized using a frequency division duplex (FDD) method so as to efficiently share the antenna. The duplexer basically includes a transmitter filter and a receiver filter. The transmitter filter is a band pass filter (BPF) passing only a frequency to be transmitted, and the receiver filter is a BPF passing only a frequency to be received. The transmitter and receiver filters pass only predetermined frequency band signals so as to efficiently share one antenna.
Efforts to fabricate such a duplexer in the form of a SoC structure have been made. As general technology for fabricating the duplexer in the form of SoC structure, a transmitter filter, a receiver filter, and a phase shifter are fabricated on a single substrate. The phase shifter generally includes a capacitor and an inductor to allow a frequency phase difference between the transmitted and received signals to be 90° so as to prevent the transmitted and received signals from being affected by each other.
However, the phase shifter isolates phases of the transmitted and received signals from each other but does not effectively intercept a physical effect such as heat or noise transmitted through a substrate. In particular, the substrate must have a very small area to fabricate the duplexer in the form of an SoC structure, and thus heat or noise is easily transmitted to another element. As a result, the whole system may make an error.